The project aims to define the functional basis of Acinetobacter baumannii intrinsic resistance to three clinically-relevant antibiotics (meropenem, colistin, and tobramycin) at a comprehensive scale. The work will identify resistance functions at genome-scale using transposon mutant sequencing, and will validate results through single mutant testing. The study will employ new technology that makes it possible to include mutants inactivating essential genes, which is usually missing from such studies. Top, validated mutants exhibiting increased sensitivity to one or more of the antibiotics will be further evaluated for whether they act through established or novel resistance mechanisms.